Gas-phase processes are used for a variety of applications, such as chemical vapor deposition processes to deposit material onto a substrate, gas-phase etching processes to remove material from a substrate or a reactor, gas-phase cleaning processes to clean a substrate or reactor, and gas-phase treatment processes to treat a surface of a substrate or a reactor. Precursors for gas-phase processes are generally selected according to a material to be deposited, etched, cleaned, or treated; i.e., the precursors are generally selected to provide desired gas-phase reactants. However, other factors are often used to select between more than one precursor that might be suitable for a particular application. For example, a reactivity or selectivity of a precursor may be a factor in the selection of the precursor. Another consideration for selecting a precursor is the stability of the precursor—e.g., does the precursor break down into other compounds before the precursor has a chance to take part in a desired reaction. Yet further considerations may include vapor pressure of the precursor, toxicity of the precursor, availability of the precursor, and cost of the precursor. Thus, a precursor that might have desirable properties, such as higher selectivity, reactivity, and/or provide more uniform deposition, etch, or treatment, may not be selected for a particular application, because the precursor is relatively expensive, has an undesirable vapor pressure, and/or is toxic.
Remote or direct plasma systems may be used to create activated or energized species from a precursor, where the energized species are more reactive than the precursor for a given reactor temperature. Remote plasma systems generally form a plasma upstream of a reaction chamber, and direct plasma systems generally form a plasma within a reaction chamber, where a substrate is often in or adjacent to the plasma. Remote plasma systems may be advantageous over direct plasma systems for some applications, because the remote plasma systems do not form a plasma directly over a surface of a substrate. As a result, surface damage to a substrate that might otherwise occur in a direct plasma reactor can be reduced or eliminated using a remote plasma. However, remote plasma activated species from many precursors are relatively short lived and recombine or react with other components before the activated species enter the reaction chamber or reach a desired area of a substrate (e.g., a lower portion of a trench formed on a surface of the substrate and/or an outer perimeter of the substrate). Using a direct plasma allows the activated species to form within the reaction chamber, but the activated species may still recombine or otherwise become inactivated prior to reacting desired areas on a substrate.
Accordingly, improved methods and systems for forming reactive species relatively close to a substrate without causing unwanted substrate damage, wherein the reactive species may be relatively stable are desired.